JP2848492B2 - Telephone - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a function of preventing a side tone of a telephone, that is, a function of preventing the output of its own transmitter from sneaking into the receiver.

[Prior Art] Most of current telephones are connected to a two-line telephone line,
This is separated into a receiver side and a transmitter side circuit by a two-wire to four-wire conversion circuit for signal transmission. Then, when the output of the own transmitter goes to the receiver side, the user's own voice can be heard from the receiver side, and a good call cannot be made.
For this reason, conventional telephones often have a side tone prevention circuit using an impedance bridge to prevent this side tone.

Therefore, a side tone prevention circuit in a conventional telephone will be described with reference to FIG. In the figure, a central office 100 has an exchange for connecting a plurality of telephone lines, and this exchange has a trunk circuit 10 for one connected telephone line. The telephone line from the telephone station 100 is connected to a telephone 300 provided in each home or the like via a telephone line 200.

Here, as shown schematically in the figure, the telephone line 200 is composed of the resistance of the telephone line itself that changes depending on the wire diameter, the distance, and the like, and the stray capacitance riding on the telephone line. For this reason,
The telephone line 200 can be equivalently represented by a resistor and a capacitor as shown.

Therefore, the central office 100 at the connection terminals L ₁ and L ₂ of the telephone 300
, The impedance of the trunk circuit 10 and the telephone line 200, that is, the line impedance Z _L seen from the telephone 300.
Is determined.

The telephone 300 has an internal circuit 12 for connecting the connection terminals L ₁ and L ₂ therein, and this internal circuit 12, the telephone line 200 and the trunk circuit 10 are connected in parallel. The connection end L ₂ is grounded, the resistance for the balance to constitute a bridge circuit (balance impedance element) R _9, R ₁₀ are connected in series to the connecting end L _2.
One end of a balance adjustment circuit 14 is connected to the connection end L1, and the other end of the balance adjustment circuit 14 is connected to a balance resistor.
It is connected to the other end of R _10. As a result, a circuit in which the balance resistors R ₉ and R ₁₀ , the balance adjustment circuit 14 and the internal circuit 12 and the external line are connected in parallel forms an impedance bridge.

The receiver 16 is connected between the connection point of the connecting end L ₂ and the resistor R ₁₀ and the balance adjusting circuit 14, transmitter 18 is the resistance R ₉
Is connected between the connection end L ₁ and the connection point of the resistors R ₁₀ and.

Therefore, if these impedances satisfy the relationship of (Z _L Z _SN ) · R ₁₀ = Z _BN · R ₉ , this impedance bridge satisfies the equilibrium condition, and the output of the transmitter 18 becomes the receiver 16. Do not get into it.

[Problems to be Solved by the Invention] In such a conventional impedance bridge, if the above-mentioned equilibrium condition is satisfied, it is possible to achieve sufficiently satisfactory sidetone prevention. But the phone
The line impedance Z _L seen from the 300 side changes greatly depending on the diameter and distance of the telephone line 200. That is, telephone line 200
Have a diameter of 0.32, 0.4, 0.5, 0.65, 0.9 mm, etc., and the loss of the signal level varies about 0 to 7 dB depending on the distance of the telephone line 200. Therefore, the installation state of the telephone 300, the line impedance Z _L of the telephone line varies considerably. However, since the balance adjustment circuit 14 in the conventional telephone is constituted by a fixed CR network,
It is not possible to cope with the impedance Z _L of the telephone line which changes greatly.

In other words, the impedance bridge satisfies the equilibrium condition because the impedance Z _{L of the} telephone line changes greatly.
And does not equilibrate under other conditions. Therefore, when the line impedance Z _L is changed, there is a problem that can not be achieved a good side tone prevention.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to provide a telephone capable of balancing an impedance bridge and obtaining good side tone prevention characteristics under a wide range of telephone line conditions. The purpose is to provide.

Means for Solving the Problems A telephone according to the present invention generates a receiver (16), a transmitter (18), an impedance measuring circuit (32), a control circuit (34), and an impedance measuring signal. A telephone set having an oscillator (40) for performing the operation, wherein the microphone (18) is connected to the impedance measurement signal input terminal (38b) and the microphone MIC.
Switch (3) having a microphone input end (38a) connected to
8), wherein the bridge circuit (36) is constituted by interconnecting the telephone internal circuit (12), the balance adjusting circuit (14) and the two balance impedance elements (R ₉ , R ₁₀ ). One of the connections (36a) between the internal circuit (12) and the balance adjustment circuit (14) is connected to the impedance measurement circuit (3
Is connected to the connecting end of a telephone line via a _{2) (L 1, L 2} ),
Its other and the connection part of (36e) and two balance impedance elements (R _9, R ₁₀₎ (36b) is connected to the transmitter (18), balance adjustment circuit (14) and the balance impedance elements (R ₁₀₎ Connection part (36c) and the telephone internal circuit (1
2) the connection between the balance impedance elements (R ₉₎ (3
6d) is connected to the receiver (16), and the oscillator (40) is connected to the impedance measurement signal input terminal (38b) of the switch (38).
When measuring the circuit impedance, the control circuit (34) switches the switch (38) to the impedance measurement signal input terminal (38b) side, and connects the oscillator (40) to the transmitter (18). The balance adjustment circuit (14) is separated from the bridge circuit (36), and at least three types of frequency signals are oscillated and supplied from the oscillator (40), and the impedance of the telephone line is measured by the impedance measurement circuit (32). Based on the measurement data of the line impedance, the impedance of the balance adjustment circuit (14) is adjusted so as to satisfy the parallel condition of the bridge circuit (36). When the telephone is normally used, the switch (38) of the transmitter (18) is used. ) To the microphone input end (38a) side, bypass the impedance measurement circuit (32), and re-install the balance adjustment circuit (14) whose impedance has been adjusted. It is characterized in that the bridge circuit (36) is connected and reconfigured.

[Operation] Since the telephone according to the present invention is configured as described above, the impedance of the telephone line can be measured by the impedance measuring circuit. Then, the impedance of the balance adjustment circuit in the bridge circuit is adjusted based on the measurement result. For this reason, even when the line impedance of the telephone line fluctuates greatly, the bridge circuit can be constantly balanced, and good sidetone prevention can be achieved.

Hereinafter, an embodiment of a telephone according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of one embodiment of a telephone according to the present invention. In the figure, connection ends L ₁ and L ₂ of the telephone line are connected to two external telephone lines, and are connected to a rectifier circuit 30 composed of a diode bridge connection. The negative connection terminal of the rectifier circuit 30 is grounded, and the positive connection terminal is connected to the impedance measuring circuit 32.

This impedance measuring circuit 32 is a balance control circuit.
According to the instruction from 34, the impedance on the telephone line side is measured as appropriate. The output side of the impedance measuring circuit 32 is connected to a bridge circuit 36 for preventing a side tone.
It should be noted that the impedance measurement circuit 32 is not normally required, so that the signal may be transmitted by bypassing the impedance measurement circuit 32.

The side bridge circuit 36 for tone prevention, the internal circuit 12 similarly to the conventional example of FIG. 8 described above, the balance adjustment circuit 14 consists of a balancing resistor R _9, R _10. The receiver 16 and the transmitter 18 are connected to the bridge circuit 36.

Here, the receiver 16 includes an operational amplifier 16a and a speaker SP.
The transmitter 18 includes a current regulator 18a, an operational amplifier 18b, and a microphone MIC. In the present invention, the microphone MIC and the operational amplifier 18b
The switch 38 is inserted and arranged between the
38 is an impedance measurement signal input terminal 38b and microphone M
An oscillator 40 having a microphone input terminal 38a for connecting an IC and generating an impedance measurement signal via the impedance measurement signal input terminal 38b can be connected to the operational amplifier 18b.

When making a normal call in the telephone configured as described above, the switch 38 of the transmitter 18 is set to the microphone input terminal 38.
Switch to the a side, bypass the impedance measurement circuit 32, and connect the balance adjustment circuit 14 to the bridge circuit 36. In this state, when the caller to the microphone MIC of the transmitter 18 to input voice, a predetermined current flows through the current regulator 18a accordingly, which via a connecting end L _1, L _2, output to the telephone line Is done. Also, the signal input from the telephone line is output from the speaker SP of the receiver 16 as voice.

In FIG. 1, a bridge circuit 36 is a telephone internal circuit.
12 and connecting end L ₁ of the one 36a of the connection portion of the balance adjustment circuit 14 and telephone line via an impedance measurement circuit 32, L ₂
The other end 36e and a connection part 36b of the two balance impedance elements R ₉ and R ₁₀ are connected to the transmitter 18, and further a connection part 36c between the balance adjustment circuit 14 and the balance impedance element R ₁₀ a connecting portion 36d of the balance impedance elements R ₉ and telephone internal circuit 12 is connected to the handset 16.

If the impedance of the bridge circuit 36 satisfies the equilibrium condition (Z _L Z _SN ) · R ₁₀ = Z _BN · R ₉ , the signal input from the transmitter 18 is not output from the receiver 16. Absent.

Here, characteristic feature in the present invention, the impedance of the telephone line telephone is connected in the impedance measuring circuit 32, that is, to be able to measure the line impedance Z _L. The measurement of the line impedance Z _L by such an impedance measurement circuit 32 is as follows.
For example, it is performed when a telephone is installed or at an appropriate timing.

This measurement is controlled by the control circuit 34.
That is, the impedance measurement signal input terminal 38b of the switch 38 is switched to the oscillator 40 side in accordance with a command from the control circuit 34, and the oscillator 40 transmits signals of at least three or more frequencies. At this time, the balance adjustment circuit 14 is disconnected from the circuit by the signal from the control circuit 34. Thus, the predetermined signal outputted from the oscillator 40 is output to the telephone line, it is possible to measure the line impedance Z _L the impedance measuring circuit 32.

Line impedance Z _L of the telephone line as measured in the impedance measurement circuit 32 in this manner is input to the control circuit 34. The control circuit 34 performs a predetermined calculation from the impedance of the telephone line to determine the resistance value and the capacitance in the balance adjustment circuit 14. Then, the resistance value and the capacitance in the balance adjustment circuit 14 are adjusted to predetermined ones by operating a switch in the balance adjustment circuit 14.

After the balance adjustment circuit 14 is adjusted in this way, the telephone returns to a normal use state, the switch 38 of the transmitter 18 is switched to the microphone input end 38a side, the impedance measurement circuit 32 is bypassed, and the impedance The adjusted balance adjustment circuit 14 is reconnected to reconfigure the bridge circuit 36.

To adjust the above manner by measuring the line impedance Z _L of the telephone line resistance and capacitance of the balance adjustment circuit 14 accordingly, the bridge circuit 36 is always impedance Z _L is to be balanced in the present invention. Therefore, it is possible to line impedance Z _L of the external telephone line to achieve consistently good side tone prevention be varied greatly.

Here the measurement of line impedance Z _L, described the measurement of line impedance Z _L. As a method of this measurement, for example, there are a resistance replacement method, a method of measuring voltage and current, and the like.

Therefore, first, the line impedance Z _L by the resistance replacement method
Will be described with reference to FIG. 2 (A). In the figure, shows the line impedance of the telephone line at the connection terminals L _1, L ₂ of the telephone 300 as schematically Z _L. And
The telephone circuit 52 for operating the telephone as a normal telephone is disconnected by the changeover switch 50, and the oscillator 40 is connected. In this example, the impedance measuring circuit 32 includes the oscillator 40 therein. In addition, as shown in FIG. 2B, a switch 50 that bypasses the impedance measuring circuit 32 may be provided in a normal state.

The impedance measuring circuit 32 has a resistor R and two voltage measuring devices 54 and 56, and the oscillator 4 of the resistor R
The voltage V ₂ after the voltage V ₁ of the 0-side and passed through the resistor R has become possible to measure. Therefore, if the oscillation signal of a predetermined frequency f by an oscillator 40, it is possible to obtain the line impedance Z _L at the frequency f from the following equation.

| Z _L | _f = R / (V ₁ / V ₂ −1) When measuring the circuit impedance Z _L by the voltage / current measurement method, as shown in FIG. A current measuring device 62 is provided on a path from the oscillator 40 to an external telephone line. Then, it is possible by the voltage V and current I are detected values of the voltage measuring device 60 and the current measuring device 62 obtains the circuit impedance Z _L by the following equation.

| Z _L | = V / I line impedance Z is _L is mean that obtaining the line impedance Z _L calculated this way, this line impedance Z _L is made from a combination of the resistance components R _1, R ₂ and the stray capacitance C ing. Therefore, the calculation of these values will be described below.

Here, the line impedance Z _L is equivalent to the circuit of the combination of the resistor and the capacitor shown in FIG. That is,
Circuit parallel connection circuit of a resistor R ₁ resistor R ₂ and capacitor C are connected in series are equivalent to the line impedance Z _L.
And, in such a circuit, so that the line impedance Z _L is different depending on the frequency f of the signal applied thereto.

The frequency characteristic of the line impedance Z _L shown in FIG. 4. Capacitors have low impedance at high frequencies and high impedance at low frequencies. Therefore, as shown in FIG. 4, at a frequency of about 300 Hz, the value of the capacitor C is almost infinite, and at a frequency of about 10 kHz, a short circuit state of almost 0Ω occurs. Therefore, 10kH
by measuring the line impedance Z _L at the time of z, it can be calculated the resistance R ₁ of the circuit.

R ₁ = | Z _L | _10k The circuit impedance Z _{L at} 300 Hz is the resistance R ₁
Has become an impedance in series connection of resistors R _2.
Therefore, a value obtained by subtracting the value of the resistor R ₁ from the line impedance Z _L at that time is the value of the resistor R _2.

_{R 2 = | Z L | 300} -R 1 Next, although determine the value of the capacitor C in the line impedance Z _L, which can be determined from the line impedance Z _L in the case of frequency 1 kHz. As shown in FIG. 4, the line impedance Z _L at a frequency of 1 kHz is a field of a parallel coupling circuit of the resistors R ₁ and R ₂ and the capacitor C. Here, the impedance of the circuit of the parallel combination of resistor R ₂ and a capacitor C and Z _C. The locus of the impedance of this circuit is as shown in FIG.

Therefore, the line impedance Z _L can be expressed as follows.

| Z _L | = (R ₁ + Z _C · cos θ) ² + (Z _C · sin θ) ² By transforming this, the following equation is obtained.

| Z _L | Meanwhile ^{_{-R 1 2 = 2 · R 1}} · Z C · cosθ + Z C 2, the resistance R ₂ and the capacitor C are connected in parallel, the impedance is shown as follows.

^{_{1 / Z C 2 = 1 /}} X C 2 + 1 / R 2 2 _{where, X C = | 1 / ω} · C | is.

Additionally, the following relationship exists for a parallel circuit of a resistor R ₂ and capacitor C.

θ = tan ⁻¹ R ₂ / X _C Therefore, the following relationship is derived.

cos θ = X _C / (X _C ² + R ₂ ² ) ^{1/2 When} X _C is obtained using this relational expression, the following is obtained.

^{_{XC = {R 2 2 · (}} Z L 2 -R 1 2) / (2 · R 2 · R 2 + R 2 2 -Z L 2
+ R ₁ ² )｝ ^1/2 Then, since ω = 2πf (f is the frequency), the value of the capacitor C is obtained as follows.

C = 1 / 2πf · {R 2 2 · (Z L 2 -R 1 2) / (2 · R 1 · R 2 +
R ₂ ² −Z _L ² + R ₁ ² )｝ ^1/2 The value of the capacitor C in the bridge circuit is obtained by substituting the value of the line impedance Z _L at the frequency of 1 kHz (f = 1 kHz) into this equation. be able to.

In this way, it is possible to determine the line impedance Z _L.

Adjustment of the impedance Z _SN of the internal circuit will not be able to its impedance for the internal circuit 12 of the telephone matching with the impedance Z _BN and other circuits in the balance adjustment circuit 36 is not in a predetermined range. In some cases, the impedance Z _SN of this internal circuit may be set to, for example, about 620Ω. in this case,
It is advisable to insert a resistor at a predetermined location in the internal circuit and adjust its value.

Adjustment of the balance adjustment circuit Z _{L In} this way, the line impedance Z _L and the internal circuit
When the impedance Z _{SN of} 12 is determined, the resistance values R ₁₂ and R ₁₁ and the capacitance C ₁₃ in the balance adjustment circuit 14 are adjusted accordingly. That is, the control circuit 34
Control the switch groups S ₁ , S ₂ , S ₃ in FIG. 6 by resistors R _{121 to} R ₁₂₄ , R _{111 to} R ₁₁₄ and the capacitor C
By appropriately adjusting the connection ₁₃₁ -C _134, adjusting the resistance value and capacitance of the balance adjustment circuit 14. For example, the value of the resistor _{R 121 ~R 124, R 111 ~R} 114 and capacitor C ₁₃₁ -C ₁₃₄ respectively 1: 2: 4: by setting the 8 resistance and capacitance 15 times the value, respectively Can be set to

The resistors R _OB , R ₁₂ , R ₁₁ ,
Examples of values of C _13, the impedance of the internal circuit 12
The following values are given in relation to Z _SN and the circuit impedance Z _L.

For example, if the balance resistors R ₉ and R ₁₀ are 10 times as large as R ₉ = 47Ω R ₁₀ = 470Ω and the resistance of the internal circuit 12 is set to 620Ω, the balance adjustment corresponding to the resistance in the internal circuit 12 The resistance R _OB in the circuit 14 may be set as follows: R _OB = 10 × Z _SN = 10 × 620 Ω = 6.2 kΩ.

The resistance R ₁₂ of the balance adjustment circuit 14, R ₁₁ and capacitor C ₁₃ resistor R _1, R ₂ of each line impedance Z _L,
The following may be determined according to the stray capacitance C.

R ₁₂ = 10 × R ₁ R ₁₁ = 10 × R ₂ C ₁₃ = C / 10 In this way, the resistance value and the capacitance in the balance adjustment circuit 14 are determined, and are set to these values by a command from the control circuit 34. You. Therefore, by adjusting the impedance of the balance adjustment circuit 14, always the bridge circuit 36 can be adjusted so as to satisfy the equilibrium condition _{(Z L Z SN) · R} 10 = Z BN · R 9.

It is also understood that by appropriately selecting the values of the balance resistors R ₉ and R ₁₀ , the resistance value of the balance adjustment circuit 14 can be easily adjusted. In the above embodiment, as a balance impedance elements, it has been adopted balancing resistors R _9, R _10, if the impedance element having a constant ratio as is apparent from the above equation, the same effect can give Can be

FIG. 7 shows a side tone prevention characteristic of the bridge circuit according to the embodiment of the present invention. In this figure, the horizontal axis shows the signal level loss (line impedance) in the telephone line, and the vertical axis shows the side tone. From this, it is understood that according to the present invention, even if the magnitude of the loss of the signal level of the telephone line changes, it is possible to always prevent a favorable side tone. According to the conventional example, when the line impedance changes, good sidetone prevention can be achieved only at one point.

Therefore, good side tone prevention can always be achieved.

This adjustment need not always be performed, and may be performed at a predetermined frequency other than when the telephone is installed.

[Effects of the Invention] As described above, according to the telephone set of the present invention, even when the impedance of the telephone line changes, it is possible to always prevent the side tone from being excellent.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a side tone prevention circuit of a telephone according to the present invention, and FIGS. 2 (A), 2 (B) and 2 (C) show a configuration showing an example of an impedance measuring circuit in the embodiment. Figure, Figure 3 is a circuit diagram showing an equivalent circuit of the line impedance Z _L, Fig. 4, a characteristic diagram showing the frequency characteristic of the line impedance Z _L, FIG. 5 is an explanatory diagram showing the trajectory of the line impedance Z _L, FIG. 6 is a circuit diagram showing an example of a balance adjustment circuit, FIG. 7 is a characteristic diagram showing a side tone prevention characteristic of the embodiment, and FIG. 8 is a block diagram showing an example of a side tone prevention circuit of a conventional telephone. . 12 Internal circuit 14 Balance adjustment circuit 16 Receiver 18 Transmitter 32 Impedance measurement circuit 34 Control circuit 36 Bridge circuit 38 Switch 40 Oscillator

Claims (1)

(57) [Claims] 1. A receiver (16), a transmitter (18), an impedance measuring circuit (32), a control circuit (34), a bridge circuit (36), and an oscillator (40) for generating an impedance measuring signal. The telephone set (18) is provided with an impedance measurement signal input terminal (38).
b) Microphone input terminal (38a) with microphone MIC connected
A bridge circuit (36) interconnecting the telephone internal circuit (12), the balance adjustment circuit (14), and the two balance impedance elements (R ₉ , R ₁₀ ). configured Te, the one connection portion of the telephone internal circuit (12) and the balance adjustment circuit (14) connected to ends of the telephone line via the (36a) an impedance measuring circuit (32) (L _1, L ₂₎ Connected, the other side (36e)
The connection part (36b) of the two balance impedance elements (R ₉ , R ₁₀ ) is connected to the transmitter (18), and the connection part (R ₁₀ ) between the balance adjustment circuit (14) and the balance impedance element (R ₁₀ ) and 36c), the connecting portion of the telephone internal circuit (12) and the balance impedance elements (R ₉₎ and (36d) is connected to the receiver (16), an oscillator (40), the impedance measuring signal input of the switch (38) The control circuit (34) connects the switch (38) to the impedance measurement signal input terminal (38b) when measuring the circuit impedance.
Side, connect the oscillator (40) to the transmitter (18), disconnect the balance adjustment circuit (14) from the bridge circuit (36), and oscillate at least three or more frequency signals from the oscillator (40) And impedance measurement circuit (32)
The impedance of the balance adjustment circuit (14) is adjusted so as to satisfy the parallel condition of the bridge circuit (36) based on the measurement data of the line impedance, and during normal use of the telephone, Switch the switch (38) of the transmitter (18) to the microphone input terminal (38a) side, and set the impedance measurement circuit (32)
The telephone that reconfigures the bridge circuit (36) by reconnecting the balance adjustment circuit (14) whose impedance has been adjusted.